The subject invention generally concerns the field of elastomer mats having raised key pads formed thereon, and specifically concerns elastomer mats that guide light from light emitting diodes to illuminate a front panel.
In modern test and measurement equipment, it is commonplace to employ light emitting diodes (LEDs) to illuminate legends printed on a Lexan(copyright) panel attached to a front panel. In such an arrangement, the LEDs are placed on an electronic circuit board (ECB) mounted behind, and parallel to, the front panel. An elastomeric mat having raised key pads formed thereon, is arranged between the ECB and the front panel. The front panel includes holes for allowing the raised keypads to protrude beyond the outer surface of the front panel for activation by a user.
When the LEDs are mounted on the rear side of the ECB, the ECB includes holes that enable light from the LEDs to travel toward the front panel. The elastomeric mat also has a hole in line with each LED to allow the light to pass unimpeded toward the front panel. The front panel also has a hole formed therein to allow the light to pass through a clear portion of the Lexan(copyright) panel.
Hollow tubes of opaque elastomeric material are formed on the mat in a substantially co-axial relationship surrounding the individual LEDs to prevent light from escaping and illuminating neighboring legends. Unfortunately, the off-axis viewing performance of this arrangement is not satisfactory because the source of the light is at the bottom of the tube, and light rays that emerge are confined to a relatively small conical area. Moreover, the off-axis viewing performance degrades even more as the tube is made longer.
One might think that using a discrete plastic light pipe at each LED would be a solution to the problem of unacceptable off-axis viewing performance. However, the discrete plastic light pipe solution does not present an attractive manufacturing solution in terms of extra components to purchase and store that require hand installation during assembly of a front panels. What is needed is a solution that improves off-axis viewing performance, but does not require extra hand-installation manufacturing steps.
An elastomeric mat is formed by extruding transparent or translucent elastomeric material into a desired shape. Columns made of the same material guide light from an LED source directly to a light port on top of the column, and diffuse the light substantially throughout the column. A coating of opaque material is used to surround the length of the columns to prevent leakage of light. When mounted adjacent to a front panel, off-axis performance is substantially increased over the prior art by, in effect, bringing the light-emitting source adjacent to a clear port of the front panel. The columns of translucent or transparent elastomeric material function as light pipes, and are formed when making the eleastomeric mat. In a further embodiment of the invention, the columns may be cylindrical or rectangular. Either a rectangular or a cylindrical column of translucent or transparent elastomeric material can convey light to illuminate a legend printed directly on top of the column.